prez23:
(means 23rd command since you logged into computer "prez").
A prompt means the other computer expects you to type a command for its "shell", or "command interpreter". The shell is the outer layer that you, the user, interact with.
Two other types of "user interfaces" you might encounter are:
o menu systems that give you choice of numbers
o "window" systems or graphical user interfaces (GUIs, pronounced "gooey").
Menu systems are popular on bulletin board services, and usually present no problem to the novice. Their weakness is that they get cloying after about five minutes. Most menu systems that are designed to be used for that length of time or longer have a "command mode", where you get—you guessed it—a shell prompt.
Even windowing systems (you know if you have one of these) very often give you a window that "emulates a terminal", i.e. that gives you a shell prompt inside.
So, you see, in each of the three common user interfaces—command line, menu-driven, or graphical user interface—you will likely encounter, at some time in your life, a shell prompt. Advice on things that will likely work to get you started is given here and in Appendix A. Some experience of other kinds of computers, especially computers that use the UNIX operating system is useful. Some tips about using UNIX and other operating systems you may not have encountered before is given in Appendix D.
If you do get stuck, whether by being experimental or just by accident, it is helpful to remember a few points: